In Ten Forward, people are gathered together and a jazz band, with Will Riker at the trombone, is playing. Deanna Troi requests that he play Nightbird – a piece Riker has been having difficulty getting right for the past ten years. He hesitantly grants her request, and just as he is about to start, Lieutenant CommanderData calls him to the bridge. Relieved, Riker goes to the bridge, where Data informs him that they will be able to transport down to the surface soon to get to the science outpost. Riker reminisces that he almost didn't make it out of there eight years ago. According to Data, they only have about 26 minutes to beam down to the planet and retrieve the database. There will be only three transport windows open altogether within the next four days, and after that, the next transport window, so Data says, will not occur for another eight years, when the planet's orbit will bring it close enough to the sun to de-phase the distortion field. Riker decides to go in ahead of schedule.

When Riker, Worf, Data and an engineer beam down to the outpost they realize that someone must have been down there. Data's tricorder detects a humanoidlifeform approaching, and much to their surprise, they find a man who looks exactly like William Riker. The duplicate claims to be Will Riker. He says that eight years ago he led a team to evacuate this station. He did not return to the USS Potemkin like the others because he was the last one out and the distortion field must have interfered with the transport. They lost the signal lock on him, and when he tried to contact the ship, he couldn't get through the interference. He asks them to check with Starfleet to confirm that he was lost that day.

Commander Riker, however, tells him that this is not what had happened. He says that in fact he himself was the last one out and that he made it back to the Potemkin. He doesn't see how both stories can be true. He wants DoctorCrusher to check him out to verify his identity.

In sickbay, Crusher informs the captain that genetically, this man is indistinguishable from Commander Riker. Since there is no evidence of genetic drift, she excludes cloning as a possible explanation. She even compares their brain scans, for brain organization patterns are as unique as fingerprints, and with only a few minor differences, she claims that they are identical. She states that brain patterns cannot be cloned either, because they are determined by experience – mostly from early childhood. CaptainPicard wonders how two grown men can share the same childhood experiences. The second Will Riker responds by insisting that he in fact is William Riker. He doesn't know who or what beamed back to the Potemkin that day but it was not him. Picard informs him that his chief engineer is checking the transporter logs of the Potemkin with the hope that it will shed some light onto the matter. In the meanwhile, he suggests that Will make himself comfortable in his quarters.

After examining the transporter logs, Geordi La Forge informs the crew that apparently there was a massive energy surge in the distortion field around the planet just at the moment Riker tried to beam out. The transporter chief at that time tried to compensate by initiating a second containment beam. However, Commander Riker's pattern maintained its integrity by just the one containment beam. And even though the second beam was shut down, somehow it was reflected back to the surface, and another William Riker materialized there. The containment beam must have had the exact same phase differential as the distortion field – hence the two identical Rikers – they both rematerialized from a complete pattern and are identical. Both of them, it seems, are the 'real' William T. Riker. The only difference between them, as Picard notes, is that they led very different lives for the past eight years and thus are very different people. He compares it to meeting one's twin and as strange as it may seem, he states that they now have two Will Rikers on board and they should do whatever they can to make the second Riker feel comfortable and welcome.

Commander Riker points out that they still have the problem of retrieving the database. Many of the station's components have been removed by Lieutenant Riker and they do not know what he did and what he changed. Picard suggests that maybe he could help them, but Dr. Crusher objects by stating that he has been alone there for a long time and that she is hesitant to let him go back until he has been fully evaluated. So, Troi suggests that she should talk to him.

When she goes to see the second Riker, he is so happy to see her that he greets her by passionately kissing and hugging her, as if the past eight years had not happened. She tells him that they need to talk and informs him that Commander Riker and she are close friends now and nothing more. The last time they saw each other, according to this Riker's memory, was at Janaran Falls on Betazed - the day before he started his tour on the Potemkin. Riker recalls that they were going to meet on Risa six weeks later. Troi interrupts him and tells him that they never did meet up in Risa. She tells him that he earned a promotion very quickly and chose to make his career a priority. There wasn't much time for anything else. They kept in touch, says Troi, but they didn't see each other again until they were both posted on the Enterprise two years later. By then, however, their feelings for each other had changed. They have now been serving together for six years but things never went back to the way they used to be.

Thomas and Deanna

Riker tells her that he had a lot of time on his hands down on that station, being mostly lonely and thinking of her. He tells her that the only way he made it through was the hope of seeing her again. He tells her that even though he knows that her feelings have changed, his have not. He can't just give up, he wants to be with her again. Troi is a little taken aback by this, wishing him a good night before she leaves.

When beaming down to the station, the two Rikers irritate each other easily and their initial interactions with one another are rather unpleasant and filled with antagonism. Lt. Riker second guesses Commander Riker's orders, causing him to raise his voice against him and reassert his position in the chain of command.

Back on the Enterprise, Troi orders a tea from the replicator and turns around to find a message on a rolled piece of paper in the fruit bowl, informing her to meet up in transporter room three. When she goes to the transporter room, she finds a flower with another message attached to it. It directs her to seek out the crystal that powers their flight – the dilithium crystal chamber in main engineering. There she finds yet another message directing her to go to Ten Forward. In Ten Forward, there is a package on the table for her to find. She opens it and finds a plate with an engraving of the Janaran Falls – the place where she and Riker spent their last night together. Riker tells her that he made it himself by using a phaser on a piece of metal and it took him three attempts.

They sit down to talk, and he admits that things are a little more complicated than he had planned. He tells her how many times he used to think about her and how in the beginning he was hoping they would find him, so he could come back to her, see her on Risa. When he finally realized that no one would come for him, he accepted his situation. He tells her that sometimes he would look up into the sky and think that if he tried hard enough, he could make her feel his presence, that he is alive, hoping that she'd wait for him. Troi confesses that she was in fact very disappointed when she and he did not meet up on Risa as they had planned. Even though she knew his career was taking him away from her, she did not want to believe it. She spent a lot of time thinking about him, wondering where he was, what he was doing. Sometimes she'd look up into the sky, and imagine that he knew and that somehow he could sense her thinking about him.

"I heard you, lieutenant. I rejected your plan."

The next day in Ten Forward, Troi has a conversation with Commander Riker. She admits that even though they both had relationships with other people, this is different. She is not sure how he feels about this and but can imagine that this must be very strange for him. Riker admits that ever since the other Will Riker has been on board, he has found himself thinking about the choices they made years ago. He doesn't mind if she chooses to be with him; however, he asks her to be careful, pointing out that if the other Riker had gotten off the planet instead of him, he probably would have made the same choices as he did. He wants her to consider that because he doesn't want her to get hurt again.

Later that day, Lieutenant Riker meets Troi in her quarters to inform her that Captain Picard has managed to get him a post on the USS Gandhi, and considering how long he has been out of commission, it is an amazing opportunity he'd like to consider. He would leave in about a week. Troi is disappointed, seeing herself hearing the same lines she heard from the other Riker eight years ago about how he has to fix his career and work first before he can be with her. This Riker assures her that he will definitely not be making the same mistake of leaving her again, but somehow Troi finds that hard to believe. It took her a long time to get over what had happened between Commander Riker and her and she does not know whether she would want to put herself in that position again. She has worked hard to make a life for herself on the Enterprise; she is happy here. He tells her that if the situation was different, he'd stay but that he cannot stay while the other Riker is aboard. Even though Troi understands, she tells him that she just does not know whether she is willing to give up her life on the Enterprise. She is willing to think about it, however. Pleased, Riker kisses her and after he leaves, Troi realizes, heartbroken again, that she is back at square one even with this version of Will Riker.

The away team successfully retrieves the data base, almost at the cost of Lieutenant Riker's life. After the Enterprise departs Nervala IV, Troi informs Lieutenant Riker of her decision to not join him on his new mission on the Gandhi. She is just not ready to give up her life on the Enterprise. While they are talking, Commander Riker comes in and gives the second Riker a trombone. Lieutenant Riker is very pleased with his decision and announces that he has decided to change his name to Thomas, his middle name. Commander Riker notes that they really are different, for he never really cared for that name. Lieutenant Riker kisses Troi one last goodbye and tells the commander to take care of her.

In the early stages of writing the episode, the production team briefly considered killing off Will Riker and having Thomas join the USS Enterprise-D's crew as his "replacement". Tom Riker would have replaced Data at operations and Data would have been promoted to first officer. The idea was quickly abandoned, partly due to the then-tentative plans to bring TNG's cast to the big screen. (Star Trek: The Next Generation Companion)

During the scene where the away team is waiting for Thomas Riker to arrive, most of the transporter control's interface is visible. However, it is completely blank, despite Lieutenant Palmer pretending to use it and the added sound effects.

As of this episode, each of the five regular male actors have worn two different colored uniforms (Burton and Dorn going from red to gold in season two, Spiner briefly wearing red in "Chain of Command, Part II", and Stewart wearing aqua during "Tapestry").

This episode reveals what Riker's middle initial ("T") stands for: Thomas. In the TNG novel Imzadi, Riker's middle initial is said to stand for "Thelonius."

Thomas Riker's dilapidated uniform, when he is first found, is in the style used by the Federation in Season 1. This would imply that this style of uniform was used for at least two years before the start of TNG. It would also correspond with Picard's memories of the Stargazer crew at the time of the Battle of Maxia in "The Battle", as well as Beverly's recollection of visiting Jack's body in "Violations", with both instances set in the 2350s, well before Riker's visit to Nervala IV.